The role of sequestering agents in softening water by complexing the "hardness" cations in water supplies is well-known. Sequestering agents are recognized aids in detergent processes because they form a soluble complex with calcium and magnesium ions which can react with soaps and other anionic surfactants and otherwise adversely affect detergency. Polyphosphates such as tripolyphosphates and pyrophosphates are widely used as ingredients in detergent compositions in part because of their property of sequestering hardness ions. Such phosphorus-containing compounds as well as nitrogen-containing compounds, e.g., nitrilotriacetates, are highly effective. However, the effect of the phosphorus content and the nitrogen content of these sequestering agents upon eutrophication of lakes and streams has been questioned and the use of phosphates in detergent compositions has been subject to government scrutiny, regulation or prohibition.
These circumstances have developed a need for highly effective and efficient phosphorus-free and nitrogen-free sequestering agents and detergency builders.
The object of the present invention is to provide such a class of compounds which are useful as sequestering agents, especially when used as builders in detergent compositions containing surfactants.
U.S. Pat. No. 3,692,685, issued Sept. 19, 1972, to Lamberti et al. discloses detergent compositions containing an ether polycarboxylate having the formula: ##STR1## wherein R is H or --CH.sub.2 COONa
U.S. Pat. No. 4,228,300, issued Oct. 14, 1980, to Lannert, discloses ether polycarboxlate sequestering agents and detergency builders having the formula ##STR2## wherein M is alkali metal or ammonium, R.sub.1 and R.sub.2 are hydrogen, methyl or ethyl and R.sub.3 is hydrogen, methyl, ethyl or COOM.
U.S. Pat. No. 3,769,223, issued Oct. 30, 1973, to Pearson et al. discloses 1-oxacyclopropane-2,3-dicarboxylic acid (i.e., epoxysuccinic acid) and its soluble salts as detergent builders.
U.S. Pat. No. 3,776,850, issued Dec. 4, 1973, to Pearson et al., discloses polymers to be used as detergent builders which are said to have the formula: ##STR3## wherein R is hydrogen or other specified radicals and n is from 2 to about 40, preferably from 2 to about 6. The polymers are taught to be prepared by polymerization of the diethyl ester of 1-oxacyclopropane-2,3-dicarboxylic acid (i.e., epoxysuccinic acid) in the presence of a boron trifluoride catalyst followed by saponification. Detergent compositions are exemplified in which n is said to have an average value of approximately 3 or 4. In fact, the disclosed synthesis method yields mixtures of materials which contain very low levels of the n=3 and n=4 components.
It is a purpose of the present invention to provide: (1) new and superior ether hydroxypolycarboxylate sequestering agents based on epoxysuccinic acid or salts thereof, (2) detergent compositions containing said sequestering agents and (3) a method for making said sequestering agents.
More specifically, it is a purpose of the present invention to provide a process which produces a high yield of ether hydroxypolycarboxylates based on oligomers of epoxysuccinates or telomers of epoxysuccinates and tartrates, effective for sequestering multivalent metal cations.